The present invention relates to an optical disk recording device and a recording signal transmission method. In particular, the present invention relates to an optical disk recording device and a recording signal transmission method that record information corresponding to a recording signal onto a recording medium by using laser light.
Optical disk recording devices typified by CDs (Compact Discs), DVDs (Digital Versatile Discs), and BDs (Blue-ray Discs) irradiate a recording medium (recording optical disk) with pulse-like laser light (hereinafter, also referred to as “recording pulse”) according to a recording signal, and records information by forming recording marks on the recording film of the recording medium. This pulse-like laser light is generated such that a laser diode driver (hereinafter, LDD) mounted in an optical pickup (CPU) drives a laser diode based on recording pulse information indicating a power level corresponding to a laser drive current and a timing tor radiating the laser light.
In each optical disk recording device, it is necessary to optimize the recording pulse depending on recording conditions such as the type of recording media, recording marks and the length of an interval (space) between the recording marks, and a recording rate. For this reason, a technique called “recording strategy” is used in which the power level of laser light is multi-valued and each edge change point of recording pulses is controlled to be small.
In recent years, in the technical field of optical disk recording devices, there is an increasing demand for lower power-consumption, downsizing, and reduction in cost, along with a higher recording rate and an increase in the number of optical disk recording devices to be mounted on portable devices. On the other hand, the recording pulse information is generated by a signal processing LSI mounted on a substrate of an optical disk recording device, and is successively transmitted to an LDD through a flexible cable by using a low voltage differential signal (hereinafter, LVDS). Additionally, in recent years, multi-value recording power levels are used, with the result that the recording pulse information to be transmitted from the signal processing LSI to the LDD is increased, which necessitates a multi-channel transmission line.
An increase in the number of channels of a transmission line hinders the miniaturization of the optical disk recording device. In general, an LVDS transmission circuit constantly uses a current of 3.5 mA per channel, which hinders the reduction in power consumption. Furthermore, while the frequency of the recording pulse information is also increased along with a higher recording rate, the transmission band is limited by the flexible cable, which hinders the improvement in the recording rate.
Japanese Unexamined Patent Application Publication No. 2009-99233 discloses a technique relating to an optical disk recording device that improves an error rate and achieves high-quality recording. FIG. 23 is a block diagram illustrating the optical disk recording device disclosed in Japanese Unexamined Patent Application Publication No. 2009-99233. The optical disk recording device disclosed in Japanese Unexamined Patent Application Publication No. 2009-99233 includes a circuit board 81, a transmission line 86, and an optical pickup 88.
The circuit board 81 includes a signal processing integrated circuit device (DSP) 82 that includes a write strategy generation circuit 83 and low voltage differential signal (LVDS) driver circuits 84 for transmitting generated write strategy signals. The optical pickup 88 includes a laser diode (LD) 91 and a laser diode driver (LDD) 89 that drives the laser diode 91. The LDD 89 includes a plurality of current sources 90. The DSP 82 included in the circuit board 81 and the LDD 89 included in the optical pickup 88 are connected together with the transmission line 86 for transmitting the write strategy signals. Differential resistors 85 are provided between differential lines at the outputs of the LVDS driver circuits 84. The LDD 89 supplied with the write strategy signals is provided with terminal resistors 87.
In the optical disk recording device disclosed in Japanese Unexamined Patent Application Publication No. 2009-99233, the provision of the differential resistors 85 between the differential lines at the outputs of the LVDS driver circuits 84 enables reduction in reflected wave generated due to an impedance mismatch of the transmission line 86. This makes it possible to provide an optical disk recording device that can improve the error rate and achieve high-quality recording.
Japanese Unexamined Patent Application Publication No. 2009-283095 discloses a technique relating to an optical disk recording device capable of reducing the number of transmission lines upon transmission of recording pulse information to a laser driver and providing high-speed recording and stable recording performance.
FIG. 24 is a block diagram showing the optical disk recording device disclosed in Japanese Unexamined Parent Application Publication No. 2009-283095. The optical disk recording device disclosed in Japanese Unexamined Patent Application Publication No. 2009-283095 includes a signal processing LSI (108), a transmission line 103, and a laser driver 104. The signal processing LSI (108) includes a recording strategy table memory 314, a recording strategy generation circuit 315, a mark/space determination circuit 120, a modulation circuit 316, an encode circuit 100, a conversion table memory 101, and an LVDS transmission circuit 102.
The laser driver 104 includes an LVDS reception circuit 105, a conversion table memory 106, a decode circuit 107, an HF generation circuit 319, a current source circuit 304, and switches 305 to 309. The laser diode 302 is driven by the laser driver 104. Then, laser light is applied to an optical disk 300, which is rotated by a spindle 301, to thereby record information onto the optical disk 300.
In the optical disk recording device shown in FIG. 24, when recording data is supplied from an upper-level host 318 to the modulation circuit 316, a recording signal NRZ from the modulation circuit 315 in the signal processing LSI (108) and a recording clock CLK synchronized with the recording signal NRZ are output to the mark/space determination circuit 120. Upon receiving the signals NRZ and CLK, toe mark/space determination circuit 120 executes determination of the mark length and the space length, and outputs mark/space information to the recording strategy generation circuit 315. The recording strategy generation circuit 315 reads our the information on the recording strategy corresponding to the received mark/space information from the recording strategy table memory 314, and generates recording pulse information L0, L1, L2, L3, and HFon.
FIG. 25 is a timing diagram showing an operation of the optical disk recording device shown in FIG. 24. Herein, a recording signal 200 shown in FIG. 25 corresponds to the recording signal NRZ output from the modulation circuit 316, and recording marks 202 indicate recording marks formed on the optical disk 300. A recording pulse 204 shown in FIG. 25 can be decomposed into timings at which recording power levels Pf, Pl, Pm, Ps, and Pc are generated and timings at which high-frequency waveforms are superimposed. The waveforms of the recording pulse information L0, L1, L2, L3, and HFon, which are output from the recording strategy generation circuit 315 to the encode circuit 100, are respectively denoted by reference numerals 205 to 208.
Each of the recording pulse information L0, L1, L2, L3, and HFon represents a power level and a change timing of a recording pulse and is input to the encode circuit 100. When each pulse state indicated by the recording pulse information L0, L1, L2, L3, and HFon is represented by a combination of bits, 5-bit 32 states can be taken as a whole (see the encode input shown in FIG. 25). However, in the case of a castle-type shown in FIG. 25 (the recording pulse shape represented by 5T Mark), when the state of each recording pulse used to actually generate the recording pulse is represented by a combination of bits, there are six states. In addition to this, as the shape of the waveform of each recording pulse, there is a recording pattern using a multi-pulse shape. However, even when the state of each recording pulse used for optical disk recording is represented by a combination of bits, about eight states can be obtained at most.
Accordingly, in the optical disk recording device shown in FIG. 24, a 5-bit encode input represented by a combination of the recording pulse information L0, L1, L2, L3, and HFon in the encode circuit 100 is encoded into a 3-bit encode output (see the encode output shown in FIG. 25). Specifically, conversion tables corresponding to the recording pulses are stored in the conversion table memory 101, and an optimum conversion table is selected according to an instruction from the recording strategy generation circuit 315 to carry out conversion in the encode circuit 100. Assume that the conversion tables stored in the conversion table memory 101 are programmably configurable using firmware for controlling the optical disk recording device.
The 3-bit encode output obtained through the conversion is converted into an LVDS signal by the LVDS transmission circuit 102. The LVDS signal thus converted is output from the signal processing LSI (108) and input to the LVDS reception circuit 105 of the LDD (104) mounted on the optical pickup through the transmission line 103 such as a flexible cable. The LVDS signal received by the LVDS reception circuit 105 is input to the decode circuit 107. The decode circuit 107 reads a conversion table similar to the conversion table used in the signal processing LSI (108) from the conversion table memory 106 within the LDD, and restores the recording pulse information of L0, L1, L2, L3, and HFon from the received encode output.
To achieve this processing, the conversion table memory 106 within the LDD is programmably configurable from a microcomputer 317 by using firmware or the like for performing control of the optical disk recording device, as with the above-mentioned conversion table memory 101, and the same contents as the conversion table memory 101 are registered. Thus, encoding the signal transmitted between the signal processing LSI and the LDD enables transmission of the pulse timing information using three coded pulses, unlike the related art in which the pulse timing information is transmitted using five recording pulse information pieces. This makes it possible to reduce the number of signal lines in the transmission line and to reduce the number of pins of the signal processing LSI and the LDD.
Moreover, according to the technique disclosed in Japanese Unexamined Patent Application Publication No. 2009-283095, a Gray code is used for encoding. The Gray code is a code for allowing bits to change in a state transition by one bit, when each code value is assumed as a state. This state transition is shown in FIG. 26. As main recording patterns that can be taken for recording pulses, there are several types including a pulse string using a multi-pulse and a pulse string of a castle-type. These recording patterns are can be applied to the state transition using the Gray code shown in FIG. 26, because a change in power level within each pulse is formed into a pattern. The 5-bit encode input shown in the timing diagram of FIG. 25 enables transmission of the recording pulse information using the Gray code through the encoding as in the encode output shown in the timing diagram of FIG. 25, Bit 0, Bit 1, and Bit 2 respectively correspond to signal waveforms 801 to 803 of the encode output when the Gray code is used. In the Gray code, the state transition always varies only by one bit, that is, only by one signal. Accordingly, the change points, i.e., edge timings, of the encode output signals do not overlap each other. Therefore, the problem involving the management of the phase and skew between bit signals can be solved.